<p>Forests store a substantial amount of organic carbon in living biomass and contribute the most to the global terrestrial carbon sink among all vegetation types. Nonetheless, the spatiotemporal variations in and drivers of forest biomass dynamics remain uncertain, especially in regions with strong human disturbances. In this study, we investigated the trends and drivers of forest biomass change in the Guangdong–Hong Kong–Macao Greater Bay Area (GBA) from 2000 to 2022 by constructing a remote sensing–based forest biomass model using the forest inventory data in the GBA. Our results indicate the forest biomass model effectively captures (R² = 0.96) the observed total forest biomass in most cities in the GBA. The total forest biomass in the GBA increased by 18.4% from 2000 to 2022, although the trend and magnitude of changes in forest biomass drastically varied across the GBA. Land use change (LUC) in the GBA induced a slight (–&#xa0;1%) decrease in forest biomass, while the rise in forest biomass density (FBD) due to tree growth and climate change contributed to a 19% increase in the total forest biomass in the GBA. LUC and FBD explained 17% and 83% of the dynamics of the total forest biomass in the GBA, respectively. Moreover, elevation, slope and temperature is the primary factors controlling the spatial variation in FBD, whereas increase in FBD across GBA over the past two decades was primarily driven by elevated atmospheric CO₂ concentrations. Overall, this study provides an effective framework to quantify forest biomass at a high spatial resolution and decipher the contributions of LUC and FBD changes to forest biomass dynamics.</p>